Gas turbine engines typically include a rotor assembly, a compressor, and a turbine. The rotor assembly includes a fan having an array of fan blades extending radially outwardly from a rotor shaft. The rotor shaft, which transfers power and rotary motion from the turbine to both the compressor and the fan, is supported longitudinally using a plurality of bearing assemblies. Known bearing assemblies include one or more rolling elements supported within a paired race. To maintain a rotor critical speed margin, the rotor assembly is typically supported on three bearing assemblies: one thrust bearing assembly and two roller bearing assemblies. The thrust bearing assembly supports the rotor shaft and minimizes axial and radial movement thereof, while the roller bearing assemblies support radial movement of the rotor shaft.
Typically, these bearing assemblies are enclosed within a housing disposed radially around the bearing assembly. The housing forms a compartment or sump that holds a lubricant (e.g., oil) for lubricating the bearing. This lubricant may also be lubricant gears and other seals. Gaps between the housing and the rotor shaft are necessary to permit rotation of the rotor shaft relative to the housing. The bearing sealing system usually includes two such gaps: one on the upstream end and another on the downstream end. In this respect, a seal disposed in each gap prevents the lubricant from escaping the compartment. Known seals include labyrinth or knife-edge seals and carbon seals.
However, the carbon seals may directly contact the moving rotor shaft, which may reduce the wear life of the seals and require dedicated cooling thereof. In this respect, many gas turbines now use hydrodynamic seals, which do not contact the rotating rotor shaft at high speed. Specifically, hydrodynamic carbon seals draw air through the seal and into the compartment, thereby maintaining a gap between the moving components and the stationary components. The pressure of air drawn into the compartment prevents the lubricant from escaping. Nevertheless, the use of two hydrodynamic seals instead of contact seals increases the size, weight, cost, and installation complexity of the bearing compartment sealing system.
Accordingly, a bearing compartment sealing system for a gas turbine engine that can provide improved wear life, reduce the volume of air drawn into the compartment during operation, and eliminate the need for dedicated seal cooling would be welcomed in the technology.